The present invention relates to a signal processing apparatus and related method, and more particularly to a signal transmitter utilizing a reference clock to up-convert two input signals with specified phase difference, and a related method.
The nonlinear characteristic of the circuit element in the signal transmitter may generate an inter-modulating distortion upon the RF signal, such that the third order inter-modulation (IM3) signal emerges around the center frequency of the RF signal. More specifically, there are two mechanisms leading to the third order inter-modulating distortion. Firstly, when the baseband signal is up-converted by a clock signal through a mixer in the signal transmitter, the nonlinearity of the mixer may induce an IM3 signal, which is sourced from the 3rd-order harmonic of the baseband signal. Secondly, when the up-converted signal is power-amplified by a power amplifying stage, such as a power gain amplifier (PGA) or a power amplifier (PA), the nonlinear operation of the power amplifying stage clock signal may also induce the IM3 signal around the center frequency of the RF signal. Furthermore, to save the power consumption of the signal transmitter, a low power supply strategic is always adopted when designing the signal transmitter; however the third order inter-modulating distortion can become worse when the signal transmitter is operated under the lower power supply. Therefore, improving the inter-modulating distortion in the transmitted signal of a signal transmitter is a significant concern in the field of wireless transceivers.